UPS surepost 4x8" labels req?

Our sales rep was telling us today that we need to print surepost on 4x8" labels. We will start shipping surepost in 2 days. Are we not going to be able to us the 4x6 termal labels? I don't see where shipstation even supports 4x8" labels.

Any feedback from people shipping surepost with shipstation please chime in on how you're doing it.
Thanks